Filter Apparatus With Porous Ceramic Plates

ABSTRACT

A filter apparatus comprises a filter stack including a plurality of porous ceramic plates that are axially spaced from one another to define plurality of axially spaced apart radial flow areas. In one example, the filter stack is mounted within a housing. In further examples, the plurality of porous ceramic plates alternate between a first set of porous ceramic plates that are nested with a second set of porous ceramic plates. In still further examples, at least one of the sides of the porous ceramic plates defines a plurality of radial flutes arranged in a radial array.

FIELD

The present disclosure relates generally to filter apparatus, and moreparticularly, to filter apparatus including porous ceramic plates.

BACKGROUND

Ceramic honeycomb filters are commonly employed to filter exhaust gases.For example, ceramic honeycomb filters are known to be used to removeparticulate and/or gases from the exhaust stream of a diesel engine.

SUMMARY

In one aspect, a filter apparatus comprises a housing including a firstfluid port and a second fluid port. A filter stack is mounted within thehousing and configured to filter a fluid stream between the fluid portswith the filter stack defining a central flow path in fluidcommunication with the first fluid port. The filter apparatus includesan outer peripheral flow path in fluid communication with the secondfluid port and defined between the filter stack and the housing. Thefilter stack includes a plurality of porous ceramic plates axiallyspaced from one another in an axial direction of the filter apparatus bya plurality of spacers to define a plurality of axially spaced apartradial flow areas. Each porous ceramic plate includes a thicknessextending between a first side and a second side of the porous ceramicplate. Each porous ceramic plate further includes a central apertureextending through the thickness of the plate, the central apertures ofthe porous ceramic plates positioned along the central flow path. Theplurality of axially spaced apart radial flow areas alternate in theaxial direction along the central flow path between a first set ofradial flow areas open to the central flow path and closed to the outerperipheral flow path, and a second set of radial flow areas closed tothe central flow path and open to the outer peripheral flow path.

In another aspect, a filter apparatus comprises a filter stack includinga plurality of porous ceramic plates that each includes a centralaperture positioned along a central flow path. The plurality of porousceramic plates are axially spaced from one another in an axial directionof the filter apparatus to define a plurality of axially spaced apartradial flow areas that alternate in the axial direction between a firstset of radial flow areas that are open to the central flow path, and asecond set of radial flow areas that are closed to the central flowpath. The plurality of porous ceramic plates alternate between a firstset of porous ceramic plates that are nested with a second set of porousceramic plates.

In yet another aspect, a filter apparatus comprises a filter stackincluding a plurality of porous ceramic plates that each include acentral aperture positioned along a central flow path. The plurality ofporous ceramic plates are axially spaced from one another in an axialdirection of the filter apparatus to define a plurality of axiallyspaced apart radial flow areas that alternate in the axial directionbetween a first set of radial flow areas that are open to the firstcentral flow path, and a second set of radial flow areas that are closedto the first central flow path. Each of the plurality of porous ceramicplates include a first side and a second side, with at least one of thesides defining a plurality of radial flutes arranged in a radial arrayabout the corresponding aperture of the porous ceramic plate to increasethe filtration surface area of the side with the radial flutes.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention are better understood when the following detailed descriptionof the invention is read with reference to the accompanying drawings, inwhich:

FIG. 1 illustrates a vertical cross-sectional view of an example filterapparatus;

FIG. 2 illustrates a cross sectional view of the filter apparatus alongline 2-2 of FIG. 1;

FIG. 3 illustrates a cross sectional view of portions of another exampleporous ceramic plate that can be used with example filter apparatus;

FIG. 4 illustrates a cross sectional view of portions of yet anotherexample porous ceramic plate that can be used with example filterapparatus;

FIG. 5 illustrates a broken away portion of another example filterapparatus;

FIG. 6 illustrates a broken away portion of yet another example filterapparatus;

FIG. 7 illustrates a cross sectional view of the filter apparatus alongline 7-7 of FIG. 1;

FIG. 8 illustrates a cross sectional view of the filter apparatus alongline 8-8 of FIG. 1;

FIG. 9 illustrates a top schematic view of another example porousceramic plate that can be used with example filter apparatus;

FIG. 10 illustrates an end view along line 10-10 of FIG. 9;

FIG. 11 illustrates a top schematic view of yet another example porousceramic plate that can be used with example filter apparatus;

FIG. 12 illustrates a vertical cross-sectional view of another examplefilter apparatus;

FIG. 13 illustrates an example filter stack including nested porousceramic plates;

FIG. 14 is a cross sectional view of the filter stack of FIG. 13;

FIG. 15 is a top view of one of a first set of porous ceramic plates ofthe filter stack of FIG. 13;

FIG. 16 is a top view of one of a second set of porous ceramic plates ofthe filter stack of FIG. 13;

FIG. 17 is a flow chart illustrating example steps of making a filterapparatus;

FIG. 18 illustrates a filter stack with a plurality of porous ceramicplates spaced from one another in an axial direction of the filter stackwith a spacing element;

FIG. 19 illustrates the filter stack of FIG. 18 after firing such thatthe plurality of porous ceramic plates are sinter bonded together withthe spacing element; and

FIG. 20 illustrates a method of fabricating a porous ceramic article.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings in which example embodiments ofthe claimed invention are shown. Whenever possible, the same referencenumerals are used throughout the drawings to refer to the same or likeparts. However, the claimed invention may be embodied in many differentforms and should not be construed as limited to the embodiments setforth herein. These example embodiments are provided so that thisdisclosure will be both thorough and complete, and will fully convey thescope of the claimed invention to those skilled in the art.

Filter apparatus are provided that can include one or more filter stacksand may include an optional housing. For example, FIG. 1 illustrates avertical cross sectional view of a filter apparatus 100 comprising afilter stack 130 mounted within a housing 110. As shown the housingcomprises a single wall housing although double wall or other wallconfigurations may be provided. A single wall housing may be desirableto allow heat transfer from the single wall to the surroundingenvironment. Heat transfer from the housing wall can be adjusted tocontrol temperature extremes and/or gradients within the filter stack130. In further examples, a double wall housing may be desirable to helpinsulate the filter stack 130 from the surrounding environment. As such,in certain operating environments, the double wall housing may beemployed to help maintain a desired maximum temperature and/ortemperature gradient of the filter stack 130.

The housing 110 may comprise a single unitary structure to provide afilter apparatus with a simplified design. Alternatively, as shown inFIG. 1, the housing 110 may be constructed from multiple parts that areconnected together. For instance, as shown, the housing includes a firsthousing portion 112 and a second housing portion 114 with correspondingflanges that may be connected together with fasteners 116.

As shown in FIGS. 1 and 2, the housing 110 can be provided with asupport plate 102 including a plate body 104 with protrusions 106designed to engage the housing 110 while defining fluid passage openings108 to allow the fluid stream 122 to pass therethrough. In furtherexamples, rather than protrusions 106, spacers may be provided toelevate the plate body to allow air passages for the fluid stream. Inexample embodiments, the support plate 102 can act as a compressionplate to help compress the filter stack 130 within the housing 110. Forexample, the fasteners 116 may be tightened to compress the filter stack130 between the second housing portion 114 and the support plate 102. Insuch examples, a first insulation layer 132 may be provided between oneend porous ceramic plate 140 and the support plate 102 and a secondinsulation layer 134 may be provided between an axially opposed endporous ceramic plate 140 and the second housing portion 114. Theinsulation layers 132, 134 can provide impact, vibrational and orthermal resistance between the filter stack 130 and other portions ofthe filter apparatus 100.

As shown in FIGS. 7 and 8, insulation ribs 135 may be provided betweenthe porous ceramic plates and the housing. As shown, the insulation ribs135 can comprise elongated strips of material positioned along the axis126. In further examples, the insulation ribs can comprise spacerblocks, spacer tabs or other constructions designed to space the porousceramic plates and the housing. The insulation ribs 135, if provided,can help position the filter stack 130 within the housing 110 to helpmaintain the outer peripheral flow path 184 and/or prevent contactbetween the porous ceramic plates 140 and the housing 110. In someexamples, avoiding contact between the porous ceramic plates 140 and thehousing 110 can be desirable to protect the porous ceramic plates fromimpact forces that may otherwise be imposed by the housing 110. Theinsulation materials forming the insulation layers and/or insulationribs may comprise compliant material capable of being deformed, such asresiliently deformed, under axial compression. In one example, thecompliant material comprises a ceramic matting material, such as aceramic paper although other materials capable of maintaining structuralintegrity under the operating temperatures of the filter apparatus 100may be used in further examples.

The housing 110 also includes a first fluid port 118 and a second fluidport 120. Either fluid port can be designed to provide an inlet and/oran outlet for a fluid stream 122. For example, as shown in FIG. 1, thefilter apparatus 100 is arranged such that the first fluid port 118provides an inlet for the fluid stream 122 while the second fluid port120 provides an outlet for the fluid stream 122. The fluid ports 118,120 may be arranged in a variety of ways. In the illustrated example,the fluid ports 118, 120 are coaxially aligned along an axis 126 of thefilter apparatus 100. In further examples, the fluid ports may beaxially offset, orthogonal, parallel or otherwise arranged with respectto one another.

As shown in FIG. 1, the filter stack 130 comprises a single filter stackmounted within the housing 110 although two or more filter stacks may beprovided in further examples. The filter stack 130 is configured tofilter the fluid stream 122 between the fluid ports 118, 120 with thefilter stack 130 defining a central flow path 180 in fluid communicationwith the first fluid port 118. As shown, the central flow path 180 maybe configured to extend along the axis 126 of the filter apparatus 100.Moreover, as demonstrated by the dashed lines 182 in FIG. 1, the centralflow path 180 may also be inwardly tapered in an axial direction 128 ofthe filter apparatus 100. In further examples, the central flow path 180may have other configurations, for example, without a taper or outwardlytapered in the axial direction. Tapering the central flow path inwardlyor outwardly in the axial direction may be selected to achieve desirablefilter efficiency while minimizing back pressure. For example, inwardlytapering the central flow path in the axial direction of the filterapparatus may reduce the back pressure during filter operation.

The filter stack 130 may be mounted within the housing 110 such that anouter peripheral flow path 184 is defined between the filter stack 130and the housing 110. In the illustrated example, the filter stack 130has an outer dimension (e.g., diameter) that is smaller than an innerdimension (e.g., diameter) of the housing 110. The filter stack 130 canbe axially aligned within the housing 110 such that the outer peripheralflow path 184 circumscribes the outer periphery of the filter stack 130.In the illustrated example, the outer peripheral flow path 184 comprisesa cylindrical area that circumscribes the outer periphery of the filterstack 130. As further shown, the filter stack 130 is mounted within thehousing 110 such that the outer peripheral flow path 184 is in fluidcommunication with the second fluid port 120.

As shown in FIG. 1, the filter stack 130 can include a plurality ofporous ceramic plates 140. Each porous ceramic plate 140 can beconsidered to include a filter profile defined between a first side 144and a second side 146 of the porous ceramic plate 140. Filter profilesof the porous ceramic plates can be defined by a wide range andcombination of characteristics of the porous ceramic plate such as:ceramic material composition, porosity and/or median pore diameter ofthe ceramic material, plate layering, catalyst loading, plate thickness,size of the central aperture and/or filter surface area of the plate,plate surface topography and/or other characteristics that impact thebackpressure, filter efficiency and/or other filter characteristics ofthe filter apparatus. In some examples, all of the porous ceramic platesare identical to one another such that each porous ceramic plateincludes substantially the same filter profile. In other examples, atleast one of the plurality of porous ceramic plates has a filter profiledefined between the first side and the second side of the porous ceramicplate that substantially changes in a radial direction of the porousceramic plate. In still further examples, at least two of the pluralityof porous ceramic plates of the filter stack have substantiallydifferent filter profiles.

The porous ceramic plates 140 can each be formed from the same materialcomposition although at least two or all of the porous ceramic platesmay comprise different material compositions. The desired materialcomposition for each plate may be selected by adjusting the ceramicforming batch material. After firing, the composition of the porousceramic plates may include a wide range of ceramic materials such asceramic/glass ceramic structures. For example, the ceramic material cancomprise a metal oxide crystalline material such as alumina, zirconia,cordierite, mullite, aluminum titanate and/or other materials. Infurther examples, the ceramic material can comprise a non-oxidecrystalline material such as silicon carbide, silicon nitride and/orother materials. In still further examples, the ceramic material cancomprise a vitreous material such as Vycor material or silica. Theceramic material can also be a glass-ceramic or may be a combination ofmaterials mentioned above.

It will be appreciated that various compositions of ceramic materialsmay be provided to obtain a porous ceramic plate with the desired filterprofile between the first side 144 and the second side 146 of the porousceramic plate 140. In some examples, all of the plates may include thesame composition of ceramic materials although two or more of the platesmay have a different composition of ceramic materials to providedifferent filter characteristics at different locations within thefilter stack. Moreover, at least one or all of the ceramic plates mayhave the same or a different material composition as a function of theradial direction from a central portion of the porous ceramic plate. Forexample, an interior portion of the porous ceramic plate may have amaterial composition that begins with one material composition at aninner portion of the plate but gradually changes to a substantiallydifferent material composition towards an outer peripheral edge of theporous ceramic plate. Providing the porous ceramic plate with adifferent material composition as a function of the radial directionfrom a central portion of the plate can provide the porous ceramic platewith a radially varying filter profile that changes the filtercharacteristics at different radial locations of the porous ceramicplate.

The porous ceramic plates 140 comprise porous ceramic material whereinthe porosity of the ceramic plates can range from about 20% to about 80%pore volume, such as from about 50% to about 70% pore volume. The mediumpore diameter of the pores can also be selected within the range of fromabout 2 microns to about 100 microns depending on the particularapplication. In still further examples, potential applications exist forlow porosity (e.g., from about 0% to about 20% pore volume), highstrength, ceramic/glass ceramic structures with unique geometries thatmay be fabricated by a 3D printing process.

It will be appreciated that various porosities and/or median porediameters may be provided to obtain a porous ceramic plate with thedesired filter profile between the first side 144 and the second side146 of the porous ceramic plate 140. In some examples, all of the platesmay include the same porosity and/or median pore diameter although twoor more of the plates may have a different porosity and/or median porediameter to provide different filter characteristics at differentlocations within the filter stack. Moreover, at least one or all of theporous ceramic plates have a porosity and/or median pore diameter thatis the same or different as a function of the radial direction from acentral portion of the porous ceramic plate. For example, an interiorportion of the porous ceramic plate may have a porosity and/or medianpore diameter that begins with at one value but gradually changes to asubstantially different value towards an outer peripheral edge of theporous ceramic plate. Providing the porous ceramic plate with adifferent porosity and/or median pore diameters as a function of theradial direction from a central portion of the plate can provide theporous ceramic plate with a radially varying filter profile that changesthe filter characteristics at different radial locations of the porousceramic plate.

Each porous ceramic plate 140 includes a thickness “T” extending betweena first side 144 and a second side 146 of the porous ceramic plate 140.A wide variety of thicknesses may be provided depending on theparticular filter application. Example thicknesses “T” can be from about10 microns to about 2,000 microns although other thicknesses may be usedin further examples. The filter profile of the porous ceramic plate 140can be substantially the same or vary between the first side 144 and thesecond side 146 of the porous ceramic plate 140. For example, as shownin FIG. 1, the material characteristics can be substantially the samethrough the thickness “T” of the material. As such, the filter profileof the porous ceramic plates of FIG. 1 remains substantially the throughthe thickness “T” of the porous ceramic plate 140. In further examples,at least one of the plurality of porous ceramic plates can includedifferent layers that have different filter profiles. For example, asshown in FIG. 3, a portion of a porous ceramic plate 240 is illustratedthat can have the similar or identical features as the porous ceramicplate 140 illustrated in FIG. 1. However, as shown, the porous ceramicplate 240 of FIG. 3 includes a first layer 240 a defining the first side244 of the porous ceramic plate 240 and a second layer 240 b definingthe second side 246 of the porous ceramic plate 240. The first layer 240a and second layer 240 b have a substantially different filter profiledefined between the first side and the second side of the porous ceramicplate. For example, as shown, the first layer 240 a has a higher medianpore diameter than the second layer 240 b. In addition or alternatively,the first layer may have a different porosity, material composition orother features to provide each layer with a different filter profile.Moreover, as shown, the thickness of the porous ceramic plate 240 isachieved by two layers although three or more layers may be provided infurther examples. Furthermore, the proportional thickness of each layermay change in the radial direction of the plates and/or the plurality ofplates in the filter stack may have different layer characteristics.

FIG. 4 a portion of a porous ceramic plate 340 is illustrated that canhave the similar or identical features as the porous ceramic plate 140illustrated in FIG. 1. Yet, the porous ceramic plate 340 of FIG. 4 isprovided with a relatively thin first layer 340 a comprising a catalystcoating of material designed to catalyze with certain gas componentsthat overlays a second layer 340 b comprising a porous ceramic materialconfigured to filter particular matter entrained in a fluid stream. Asshown, the catalyst is provided as a coating over the porous ceramicmaterial. In further examples, the catalyst can be impregnated withinthe porous ceramic material. In still further examples, the plates maybe formed from nano-catalyst particles using a binder. The material canthen be fired at a sufficiently high enough temperature so as not tocause the catalyst particles to sinter (e.g., at a temperature of lessthat 1100° C.). The catalyst materials may consist of catalyst suitablefor NOx removal such as a metal catalyzed zeolites or a metal oxide ormixed metal oxide to promote oxidation of soot and gas species. Suchcatalyst application may be provided at different concentrations withineach plate as a function of the radial direction of the plates and/ormay be provided at different concentrations at different plates withinthe filter stack.

As shown in FIG. 1, the thickness “T” of each porous ceramic plate 140of the filter stack 130 is substantially identical such that thethickness does not impact any difference in filter profiles of theceramic plates. In further examples, at least one of the plates of thefilter stack can be provided with a thickness that is different than oneor more of the remaining plates. For instance, the plates may have athickness that is successively less or greater than one another in theaxial direction to change the filter profile of each plate and thereforeprovide desired filtering characteristics throughout the filter. Forexample, FIG. 5 illustrates a broken away portion of another filterstack 430 wherein the thickness “T” of the plurality of porous ceramicplates 440 is successively smaller than one another in the axialdirection 428.

As further illustrated in FIG. 1, the porous ceramic plates also have athickness “T” that is substantially constant in the radial direction. Infurther examples, one or more of the disks may have a variable thickness“T” in the radial direction to change the filter profile of the porousceramic plate in the radial direction. The thickness of the porousceramic plate may increase or decrease in the radial direction. Forexample, FIG. 6 illustrates broken away portion of another filter stack530. As shown the thickness “T₁” at the inner periphery of the centralaperture 542 is less than the thickness “T₂” at the outer peripheraledge 548 of the porous ceramic plate 540. Indeed, the thickness of theporous ceramic plate 540 constantly increases in the radial direction127 extending away from the axis 526 of the filter stack 530. Inalternative examples, the thickness can constantly decrease in theradial direction.

Each porous ceramic plate 140 further includes a central aperture 142extending through the thickness “T” of the plate. As illustrated, thecentral apertures 142 of the porous ceramic plates 140 can be positionedalong the central flow path 180. As further shown, in more particularexamples, the central apertures 142 may be axially aligned with respectto one another along the axis 126 of the filter apparatus 100.

The central apertures 142 can comprise a wide range of shapes and sizesdepending on the filter application. Moreover, the porous ceramic plates140 can have an outer peripheral edge 148 that can also likewise beprovided with various shapes and sizes. The shapes of the aperturesand/or outer peripheral edges can be circular, elliptical or otherwisecurvilinear and/or comprise various polygonal shapes such as triangular,rectangular (e.g., square) or other polygonal shapes. In one example,the central aperture 142 and outer peripheral edge 148 of thecorresponding porous ceramic plate 140 are geometrically similar to oneanother although the shapes may be geometrically different in furtherexamples. For instance, as shown in FIGS. 7 and 8, the illustratedapertures 142 comprise circular apertures that are concentric withgeometrically similar circular peripheral edges 148 of the porousceramic plate 140.

The sizes of the central apertures 142 and outer peripheral edges 148may also vary with respect to one another depending on the filterapplication and/or the location of the plate within the housing 110. Forexample, as shown in FIG. 7, the outer peripheral edges 148 can includea transverse dimension (e.g., diameter “D”) transverse to the axis 126of the filter apparatus 100 in a range from about 3 cm to about 50 cmalthough other sizes may be provided in further examples. Moreover, thecentral aperture 142 can include a transverse dimension (e.g., diameter“d”) in a range from about 3% to about 80% of the transverse dimension(e.g., diameter “D”) of the corresponding outer peripheral edge 148 ofthe porous ceramic plate 140.

The central apertures of the plates may have the same size although oneor more of the apertures may have a different size in further examples.Example filter stacks may further include apertures that successivelydecrease or increase in size in the axial direction. For example, asshown in FIG. 1, the central apertures 142 of the plurality of porousceramic plates 140 are successively smaller than one another in theaxial direction 128. The successively smaller apertures help define thecentral flow path 180 that is inwardly tapered in the axial direction128. As such, the first and second sides of the plurality of porousceramic plates 140 have corresponding filter surface areas that aresuccessively larger than one another in the axial direction 128. Thesuccessively smaller apertures and/or the successively larger surfaceareas of the porous ceramic plates provide each successive plate with adifferent filter profile that can help improve the filter efficiencyand/or back pressure characteristics of the filter apparatus 100.Although not shown, successively larger filter surface areas can also beprovided in alternative ways. For example, the outer peripheral edge 148may be successively larger in the axial direction. In further examples,of beginning plates may be flat while successively changing surfacetopography to increase the effective filtering surface area of theplates in the axial direction as described below.

As shown in FIGS. 1, 7 and 8, the porous ceramic plates 140 may comprisea disk that has a relatively thin thickness “T” when compared to atransverse dimension (e.g., diameter “D”) of an outer peripheral edge148. Indeed, as shown in FIG. 1, the disk may a substantially flat platewith a substantially flat filter surface topography on the first side144 that may be parallel a substantially flat filter surface topographyon the second side 146 of the disk. In further examples, at least one ofthe porous ceramic plates may have one or more filter surfaces that arenot substantially flat that increase the surface filtration area of theplate. For instance, at least one of the first side 144 and the secondside 146 may have a surface topography including bumps, divots, flutes,ribs and/or the like. Providing surface topographies that are not flatmay increase the surface area of the porous ceramic plate to helpincrease the filtering efficiency. Moreover, a combination plates withdifferent degrees of non-flat surface topographies may help fine tunethe filter profile of each individual plate in the axial direction.

FIGS. 9 and 10 illustrate a first example of a porous ceramic plate 640that may comprise the same or identical porous ceramic material andotherwise have similar or identical characteristics as the porousceramic plates described above. However, unlike the example porousceramic plates described above, the porous ceramic plate 640 of FIGS. 9and 10 includes a first side 644 and a second side 646 that do not havesubstantially flat surface topographies. Indeed, the first side 644includes a plurality of radial flutes 645 arranged in a radial arrayabout a corresponding central aperture 642 of the porous ceramic plate640. The example radial flutes 645 are defined between correspondingradial peaks 644 a and corresponding radial valleys 644 b. The radialpeaks 644 a and radial valleys 644 b are respectively representedschematically by solid and dashed radial lines in FIG. 9. Likewise, thesecond side 646 also includes a plurality of radial flutes 647 arrangedin a radial array about the corresponding central aperture 642. As shownby FIGS. 9 and 10, the surfaces defining the radial flutes 645, 647 maybe provided by a filter surface that undulates about the correspondingcentral aperture. As shown in FIGS. 9 and 10 the undulating surface mayfollow a sinusoidal function about the corresponding central aperture.Indeed, the illustrated surface is shown to be wavy to present asinusoidal wave that is arrayed about the central aperture 642. Infurther examples, the wave may comprise a square wave or angular wave orother wave shapes. Furthermore, the flutes may appear as grooves orother radial configurations formed in the surface of the porous ceramicplate.

If provided, the plurality of radial flutes can have a first number ofopenings at an outer periphery that is greater than or equal to a secondnumber of openings at the inner periphery defining the central apertureof the porous ceramic plate. For example, as apparent in FIGS. 9 and 10,the radial flutes 645, 647 have a first number of openings the outerperipheral edge 648 that is the same as a second number of openings atan inner periphery defining the central aperture 642. FIG. 11illustrates another example porous ceramic plate 740 similar to theporous ceramic plate 640 shown in FIGS. 9 and 10, but having a pluralityof flutes (corresponding to each side of the plate) that split radiallysuch that the first number of openings at the outer peripheral edge 748is greater than a second number of openings at the inner peripherydefining the central aperture 742. The flutes 745 corresponding to thefirst side 744 are described with the understanding that such discussionalso applies to the flutes corresponding to the second side (not shown)such that the profile view of the edge would be substantially identicalto FIG. 10 with three times as many flutes open at the outer peripheraledge 748. As shown in FIG. 11, the flutes 745 are divided three wayssuch that a plurality of radial inner flutes 745 a each have a singleopening at the inner periphery defining the central aperture 742. Eachof the flutes 745 radially splits into a corresponding three radialouter flutes 745 b, 745 c, 745 d although the flutes may divide into twoor more than three radial outer flutes in further examples. Providingflutes with increased openings at the outer periphery, as shown in FIG.11, can further increase the surface area of the porous ceramic disk byinhibiting dilution of the density of flutes in the radial directionthat is observed with the wavy disk design illustrated in FIGS. 9 and10. Moreover, alternative divided arrangements may be provided infurther examples. For instance, in alternative examples, all of thepeaks at the outer peripheral edge 748 of the first side can reach thesame height (like shown in FIG. 10). Likewise, all of the peaks at theouter peripheral edge 748 of the second side can also reach the samedepth (like shown in FIG. 10). Indeed, the end view of the dividedflutes shown in FIG. 11 can appear substantially identical to FIG. 10wherein the sinusoidal function has three times the frequency since theflutes are divided three ways.

Turning back to FIG. 1, the porous ceramic plates 140 are axially spacedfrom one another in the axial direction 128 by a plurality of spacers todefine a plurality of axially spaced apart radial flow areas. Theplurality of axially spaced apart radial flow areas alternate in theaxial direction 128 along the central flow path 180 between a first setof radial flow areas 150 open to the central flow path 180 and closed tothe outer peripheral flow path 184, and a second set of radial flowareas 152 closed to the central flow path 180 and open to the outerperipheral flow path 184.

As shown in FIGS. 1 and 8, the plurality of spacers include a first setof spacers 160 that close the outer peripheral flow path 184 from afirst set of radial flow areas 150. Moreover, as shown in FIGS. 1 and 9,the plurality of spacers include a second set of spacers 162 that closethe central flow path 180 from the second set of radial flow areas 152.In one example, the spacers can comprise compliant spacers althoughsubstantially rigid spacers may be used in further example. Compliantspacers, if provided, are capable of being deformed, such as resilientlydeformed, under axial compression. In one example, the compliantmaterial comprises a ceramic matting material, such as a ceramic paperalthough other materials capable of maintaining structural integrityunder the operating temperatures of the filter apparatus 100 may be usedin further examples. As shown in FIG. 1, providing the spacers ascompliant spacers allows the filter stack to be compressed in the axialdirection, e.g., by way of fasteners 116, while the compliant spacersaxially bias the respective porous ceramic plates from one another tomaintain the respective spacing between the porous ceramic plates. Infurther examples, the spacers may comprise a sealing material, adhesiveor other material configured to space the ceramic plates from oneanother. Moreover, the spacers may be provided separately or may beformed integrally with the plates. In further examples the spacers(e.g., compliant spacers) may be attached to one of the porous ceramicplates before creating the filter stack. For example, the spacers may beattached by printing the spacers on the corresponding porous ceramicplate.

The radial flow areas 150, 152 can each have identical widths definedbetween a corresponding pair of the porous ceramic plates, althoughdifferent widths may used in further examples depending on the filterapplication. For example, the axial width of at least one of the firstset of radial flow areas may be greater than the axial width of at leastone of the second set of radial flow areas. As shown in FIG. 1, theaxial width of each radial flow area of the first set of radial flowareas 150 is greater than the axial width of each radial flow area ofthe second set of radial flow areas 152. Providing a greater axial widthfor the first set of radial flow areas can accommodate particulate buildup on the walls as the fluid stream passes through the porous ceramicplates from the first set of radial flow areas 150 to the second set ofradial flow areas 152. The axial width of the radial flow areas can bein a range from about 50 microns to about 2000 microns although otherwidths may be provided in further examples.

Optionally, at least one of the plurality of spaced apart radial flowareas may be divided into a plurality of radial flow channels arrangedin a radial array about the central flow path. Dividing the radial flowareas into a plurality of radial flow channels can help radially directthe path of the fluid stream passing between respective porous ceramicplates. In the illustrated example, each of the radial flow areas isdivided into a plurality of radial flow channels arranged in a radialarray about the central flow path. For example, as shown in FIG. 8, thefirst set of radial flow areas 150 may be divided into a plurality ofradial flow channels 150 a by radial divider walls 151. Likewise, asshown in FIG. 7, the second set of radial flow areas 152 may be dividedinto a plurality of radial flow channels 152 a by radial divider walls153. The divider walls 151, 153 can comprise various materials. In oneexample, the divider walls 151, 153 comprise substantially the samematerial as used to form the compliant spacers 160, 162.

FIG. 12 illustrates a vertical cross-sectional view of another examplefilter apparatus 800. The filter apparatus 800 can include many of thefeatures described with respect to the filter apparatus 100 describedabove. Indeed, the filter apparatus may include the same housing 110,support plate 102 and insulation layers 132, 134 although alternativeconfigurations may be provided in further examples. As shown in FIG. 12,the housing may be provided with a first unitary filter stack 830 a anda second unitary filter stack 830 b that are axially aligned with oneanother along the axis 826 of the filter apparatus 800. Although twofilter stacks are illustrated in FIG. 12, three or more stacks may beprovided in further examples. Each unitary filter stack 830 a may have aplurality of porous ceramic plates 140 that may be of any configurationdiscussed above. However, the porous ceramic plates 140 are integrallyconnected to one another by spacers 860. The spacers 860 may comprisematerial designed to sinter bond the porous ceramic plates togetherduring a firing of the filter stack as described more fully below.

As shown, a layer of material 836 may be provided between the filterstacks 830 a, 830 b and may comprise a compliant material similar to theinsulation layers 132, 134. The layer of material 836 can help preventdamage or noise that may otherwise be generated if the filter stackswere able to impact one another in response to external forces.

FIG. 13 illustrates another example filter stack 930 that can be used,for example, with various filter apparatus set forth in this disclosure.For example, the filter stack 930 can be used with features describedwith respect to the filter apparatus 100, 800 described above. Forinstance, the filter stack 930 can include the same housing 110, supportplate 102 and insulation layers 132, 134 although alternativeconfigurations may be provided in further examples. Furthermore, thefilter stack 930 may comprise a unitary filter stack used alone or incombination with other filter stacks.

FIG. 14 is a cross-sectional view of the filter stack 930 of FIG. 13. Asshown, the plurality of porous ceramic plates alternate in an axialdirection 982 of the filter stack 830 between a first set of porousceramic plates 940 a that are nested with a second set of porous ceramicplates 940 b. The porous ceramic plates 940 a, 940 b can include similaror identical features (e.g., filter profile, material type, etc.) as theporous ceramic plates 140 described above.

FIG. 15 illustrates a top view of one of the first set of porous ceramicplates 940 a. As shown in FIG. 15, the top of the plate may have aplurality of ribs (that are not shown in the cross section of FIG. 14for clarity). The plurality of ribs can include a wide range ofconfigurations. In the illustrated example, the ribs include a first setof ribs 951 a radially spaced around the central aperture 942 a and asecond set of ribs 953 a that are also radially spaced around thecentral aperture 942 a with each rib of the second set of ribs 953 a bepositioned between a corresponding pair of ribs of the first set of ribs951 a. As shown, the ribs of the second set of ribs 953 a may be shorterthan the ribs of the first set of ribs 951 a although identical riblengths may be provided in further examples. Still further, each rib ofthe first and second set of ribs 951 a, 953 a can include an enlargedend 955 designed to provide additional area for sintering as discussedbelow. As further illustrated, the first set of ribs 951 a extend to acentral collar member 970. The central collar member 970 can include anouter peripheral portion 972 and an inner peripheral portion 974. Asshown in FIG. 14, the outer peripheral portion 972 can include a landing973 positioned a height “H₁” from the top surface 981 a. In theillustrated example, the first and second set of ribs 951 a, 953 a andthe enlarged end 955 also have the same height “H₁” from the top surface981 a. The outer peripheral edge 948 a can also be provided with analignment tab 976 a for alignment with other parts of the filter stackand/or the housing.

FIG. 16 illustrates a top view of one of the second set of porousceramic plates 940 b. As shown in FIG. 16, the top of the plate may havea plurality of ribs (that are not shown in the cross section of FIG. 14for clarity). The plurality of ribs can include a wide range ofconfigurations. In the illustrated example, the ribs include a first setof ribs 951 b radially spaced around the central aperture 942 b and asecond set of ribs 953 b that are also radially spaced around thecentral aperture 942 b with each rib of the second set of ribs 953 b bepositioned between a corresponding pair of ribs of the first set of ribs951 b. As shown, the ribs of the second set of ribs 953 b may be shorterthan the ribs of the first set of ribs 951 b although identical riblengths may be provided in further examples. As further illustrated, thefirst and second set of ribs 951 b , 953 b extend to an outer peripheralspacing element 990. The outer peripheral spacing element 990 caninclude an outer peripheral portion 992 and an inner peripheral portion994. As shown in FIG. 14, the inner peripheral portion 994 can include alanding 995 positioned a height “H₂” from the top surface 981 b. In theillustrated example, the first and second set of ribs 951 b, 953 b alsohave the same height “H₂” from the top surface 981 a. The outerperipheral edge 948 b can also be provided with an alignment tab 976 bfor alignment with other parts of the filter stack and/or the housing.

As shown in FIG. 14, each porous ceramic plate of the first set ofporous ceramic plates 940 a includes an outer peripheral edge 948 aconfigured to nest within a corresponding porous ceramic plate of thesecond set of porous ceramic plates 940 b. For example, as shown, abottom surface 983 a of the first set of porous ceramic plates 940 a areconfigured to rest against the landing 995 and the top surface of theribs 951 b, 953 b. Moreover, the outer peripheral edge 948 a is nestedwithin a groove 991 formed between the landing 995 and the outerperipheral portion 992.

Moreover, the central collar portion 970 of each of the first set ofporous ceramic plates 940 a may be configured to nest with the centralaperture 942 b of a corresponding plate of the second set of porousceramic plates 940 b. For example, as shown, the second set of porousceramic plates 940 b each include a bottom surface 983 b configured torest against the landing 973 and the top surface of the ribs 951 a, 953a. Moreover, an inner surface defining the central aperture 942 b isconfigured to nest within a groove 993 formed between the landing 973and the inner peripheral portion 974. The central collar portion 970 maybe configured to be received within the central aperture 942 b of acorresponding porous ceramic plate of the second set of porous ceramicplates 940 b. For example, as shown, the inner peripheral portion 974 ofthe central collar member 970 may be received within the centralaperture 942 b while the bottom surface 983 b of the second set ofporous ceramic plates 940 b rest against the landing 973 and the topsurface of the ribs 951 a, 953 a.

As shown in FIG. 13, the plates may be stacked such that thecorresponding alignment tabs 976 a, 976 b are aligned along the axialdirection 982. Once stacked, the vent openings 932 are defined betweencorresponding enlarged ends 955 of the first and second set of ribs 951a, 953 a.

As shown, the top surfaces 981 a, 981 b and the bottom surfaces 983 a,983 b of each of the plates is substantially flat although othersurfaces may be provided in further examples as described with respectto other example porous ceramic plates of the disclosure.

The first and second sets of porous ceramic plates 940 a, 940 b may befabricated by various techniques such as stamping, molding, 3D printingtechniques typically used for rapid prototyping, or the like. Moreover,the plates may be fired before or after building the filter stack 930.For example, a ceramic-forming material may be produced into the generalconfiguration of the plates 940 a, 940 b. The plates may then be driedand fired to produce the first and second sets of porous ceramic plates940 a, 940 b. The porous ceramic plates 940 a, 940 b may then be stackedas shown in FIG. 14 with a sintering material applied between theplates. For example, a slurry of sinter forming material may be painted,sprayed or otherwise applied to the intersecting surfaces of the plates.In further examples, portions of the plates may be dipped into a slurrybath of sinter forming material. For instance, the first plurality ofporous ceramic plates 940 a may be inverted and dipped into a slurrybath to coat the inner peripheral portion 974, the landing 973, the topsurfaces of the ribs 951 a, 953 a (including enlarged ends 955).Likewise, the second plurality of porous ceramic plates 940 b may beinverted and dipped into a slurry bath to coat the outer peripheralportion 992, the landing 995 and the top surfaces of the ribs 951 b, 953b with sinter forming material. Once stacked, as shown in FIG. 14, thefilter stack 930 may then be fired again wherein the coating of materialsinters together the porous ceramic plates 940 a, 940 b. In alternativeembodiments, the filter stack may be designed to operate without asecond firing step. For example, the plates may be attached to oneanother with an adhesive material. In further examples, a compliantmaterial may be provided between the plates and the filter stack maythen be compressed within a housing using techniques similar to thosedisclosed with respect to the filter stack 130 illustrated in FIG. 1.

FIG. 17 is a flow chart illustrating example steps of making a filterapparatus. In order to make the filter apparatus 100 illustrated in FIG.1, the method may include the step 1000 of providing a plurality ofplates with a central aperture, wherein each plate is formed from aceramic-forming material.

After the step 1000 of providing the plates, the method then includesthe step 1002 of firing the plurality of plates to form the plurality ofporous ceramic plates 140 that each includes the central aperture 142.The same or similar firing procedure may be performed to form any porousceramic plate in accordance with the present disclosure including butnot limited to the porous ceramic plates 240, 340, 440, 540, 640, 740also described above.

The method can then include the step 1004 of creating the filter stack130 by axially spacing the porous ceramic plates 140 from one another inthe axial direction 128 with the plurality of compliant spacers 160, 162to define a plurality of axially spaced apart radial flow areas 150,152. The central apertures 142 of the plurality of porous ceramic plates140 are positioned along the central flow path 180. Moreover, the radialflow areas alternate in the axial direction 128 between the first set ofradial flow areas 150 that are open to the central flow path 180, andthe second set of radial flow areas 152 that are closed to the centralflow path 180.

The method can then include the step 1006 of mounting the filter stack130 within the housing 110 such that the first fluid port 118 is influid communication with the central flow path 180 and the second fluidport 120 is in communication with the outer peripheral flow path 184defined between the filter stack 130 and the housing 110. Once mounted,the first set of radial flow areas 150 are closed to the outerperipheral flow path 184 and the second set of radial flow areas 152 areopen to the outer peripheral flow path 184.

Optionally, method can further include the step 1008 of compressing thefilter stack 130. For example, the second housing portion 114 and thefirst housing portion 112 can be clamped together with the fasteners 116to compress the filter stack 130 in the axial direction 128 while thecompliant spacers 160, 162 axially bias the respective porous ceramicplates 140 from one another to maintain the respective spacing betweenthe porous plates. In the illustrated example, the housing is used tocompress the filter stack but a compressing arrangement separate fromthe housing may be used in further examples.

The flow chart of FIG. 17 also illustrates steps of making the filterapparatus 800 illustrated in FIG. 12. In order to make the filterapparatus 800 illustrated in FIG. 12, the method may include the step1000 of providing a plurality of plates with a central aperture, whereineach plate is formed from a ceramic-forming material. After the step1000 of providing the plates, the method then includes the step 1002 offiring the plurality of plates to form the plurality of porous ceramicplates 140 that each includes the central aperture 142. The same orsimilar firing procedure may be performed to form any porous ceramicplate in accordance with the present disclosure including but notlimited to the porous ceramic plates 240, 340, 440, 540, 640, 740 alsodescribed above.

Next, the method includes can further include the step 1010 of creatinga first filter stack 829 depicted in FIG. 18. The first filter stack 829is formed by axially spacing the first plurality of porous ceramicplates 140 from one another in the axial direction 128 of the filterapparatus with a first spacing element 859 to define a first pluralityof axially spaced apart radial flow areas. The first spacing element 859may comprise a layer of material configured to sinter bond the porousceramic plates together during a subsequent firing procedure. Examplematerials for the first spacing element 859 may comprise glass fritsealing, inorganic binder cement such as aluminum phosphate or othermaterials. The central apertures 142 of the first plurality of porousceramic plates 140 are positioned along a first central flow path 880 a,and the radial flow areas alternate in the axial direction of the firstfilter stack between a first set of radial flow areas 850 a that areopen to the first central flow path 880 a, and a second set of radialflow areas 852 a that are closed to the first central flow path 880 a.

Once the first filter stack 829 is formed, the first filter stack maythen be subsequently fired during method step 1012 to sinter bond thefirst plurality of porous ceramic plates 140 together with the firstspacing element 859. After firing step 1012, the first unitary filterstack 830 a is formed as shown in FIG. 19, wherein the first spacingelement 859 is integrally bonded between the porous ceramic plates 140to form the first and second set of radial flow areas 850 a, 850 b.Although not shown in FIG. 18, spacer ribs may be provided to helpmaintain the space between the plates while the first spacing element859 sinter bonds the plates together. For instance, in one example, theporous ceramic plates 140 may be formed of a material including mullitewhile the spacing elements 859 may be formed of cordierite. Thecordierite material has a lower melting point than the mullite porousceramic plates 140. As such, the plates may be bonded together at alower firing temperature (e.g. less than 100° C.) wherein the ceramicmaterial 859 may begin melting and infiltrating into the pores of theporous mullite ceramic plates. While the ceramic material spacingelements 859 become compliant during the melting process, the spacers(not show) maintain the spacing between the plates. After the firingprocess, the filter stack forms a unitary structure wherein thecordierite spacing elements are integrated with the porous mullitematerial to form a desirable seal. The spacers (not shown) used incombination with the spacing elements 859 can, for example, compriseradial ribs similar in shape as the ribs 951 a, 951 b, 953 a, 953 bdescribed with respect to FIGS. 15 and 16 above. The spacers may beintegral ribs or spacers attached (e.g., by printing) or otherwiseplaced between the plates.

At the same time or after forming the first unitary filter stack 830 a,the second unitary filter stack 830 b may be formed by a similarprocedure. Indeed, the same steps 1000 and 1002 can be carried out toprovide a second plurality of porous ceramic plates that may beidentical to the first plurality of porous ceramic plate. Moreover, themethod can include the step 1014 of creating the second filter stackthat may be identical to the first filter stack 829 illustrated in FIG.18. Indeed, the second filter stack, similar to the first filter stack829, may be created by axially spacing the second plurality of porousceramic plates (e.g., identical to the first plurality of porous ceramicplates) from one another in the axial direction of the second filterstack with a second spacing element (e.g., identical to the firstspacing element) to define a second plurality of axially spaced apartradial flow areas. The central apertures of the second plurality ofporous ceramic plates are positioned along a second central flow path,and the second plurality of radial flow areas alternate in an axialdirection of the second filter stack between another first set of radialflow areas that are open to the second central flow path, and anothersecond set of radial flow areas that are closed to the second centralflow path. Once the second filter stack is formed, the method canfurther include a similar firing step 1012 to sinter bond the secondplurality of porous ceramic plates together with the second spacingelement to provide the second unitary filter stack 830 b. In certainfiring method steps 1012, the first and second unitary filter stack 830a, 830 b may be formed during the same firing procedure or may be formedduring separate firing procedures.

Once fired, the first unitary filter stack 830 a and/or the secondunitary filter stack 830 b may be mounted within the housing 110 duringmethod step 1006. Once mounted, the first fluid port 118 will be influid communication with the first central flow path 880 a and a secondfluid port 120 will be in communication with the outer peripheral flowpath 184 defined between the first filter stack 830 a and the housing110. If provided with a second unitary filter stack 830 b, the first andsecond filter stacks 830 a, 830 b can be mounted in series within thehousing 110 as shown in FIG. 12. Once mounted, the first and secondcentral flow paths of the first and second filter stacks 830 a, 830 bare in fluid communication with one another. Moreover, the first fluidport 118 will be placed in fluid communication with the central flowpaths of the first and second filter stacks 830 a, 830 b and a secondfluid port 120 will be placed in fluid communication with the outerperipheral flow path defined between the filter stacks and the housing.Once mounted, the first sets of radial flow areas will be open to thecentral flow paths and closed to the outer peripheral flow path, and thesecond sets of radial flow areas will be closed to the central flowpaths and open to the outer peripheral flow path.

After the method step 1006 of mounting, the first and second filterstacks 830 a, 830 b may be optionally compressed within the housingduring method step 1008.

A method of operating the filter apparatus will now be described withrespect to the filter apparatus 100 described in FIG. 1 with theunderstanding that the same operation may also apply to the filterapparatus 800 illustrated in FIG. 12. In operation, a fluid stream 122enters the first fluid port 118 of the housing 110. The fluid streamthen travels down the central flow path 180 in the axial direction 128toward the second fluid port 120. The first set of radial flow areas 150are open to the central flow path 180. As such, the fluid stream 122eventually passes from the central flow path 180 to radially traveloutward and into one of the radial flow areas of the first set of radialflow areas 150. The fluid stream 122 then passes through one of theporous ceramic plates 140 to enter one of the radial flow areas of thesecond set of radial flow areas 152. The porous ceramic plates filterparticular matter from the fluid stream as the fluid stream passes fromthe first set of radial flow areas 150 to the second set of radial flowareas 152. Moreover, if catalytic material is provided, gases may alsobe removed from the fluid stream. The second set of radial flow areas152 are open to the outer peripheral flow path 184. As such, thefiltered fluid stream eventually travels through the second set ofradial flow areas 152 to the outer peripheral flow path 184. Thefiltered fluid stream then travels along the outer peripheral flow path184 and out the second fluid port 120.

In further examples, a method of creating a filter stack similar to thefilter stack shown in FIG. 19 can first include the step of forming aplurality of plates from with a composition comprising catalystparticles and a binder material. The catalyst materials can comprisecatalyst suitable for NOx removal such zeolite or aluminosilicatematerial, ceria-zirconia, alumina, pervskites, spinel, titania, ceriaand zirconit. In addition, these materials may be impregnated with atleast one precious metal from the group Pt, Pd, & Rh to further lowerthe soot regeneration temperature. On one example, the metal catalyzedzeolites may be used, e.g., M-Beta, M-Chabazite, M-ZSM5, M-Mordenite,M-MCM-4, M-Ferrerite, M-NaY & M-USY. M may represent Fe, Cu, Ce, Co, Pt,Rh & Pd. In one example, the exchange of the metal can be between 0.5%and 6%. The zeolite silicate/alumina range can be grater than 10 and thedisks can constitute combinations of these M-zeolite materials withdifferent porosity and MPS range. Porosity may range from 30%-80% andMPS 1-50 microns. Alternatively, suitable precursor composition whichmay undergo a hydrothermal treatment to form such metal exchangezeolites as listed above may be used.

The plurality of plates can be fired without sintering a substantialamount of the catalyst particles. The filter stack can be created. Inone example, the entire filter stack is fired together such that thefilter stack forms a unitary structure. In other examples, the filterstack includes compliant spacers as described above.

The plates can be made by 3D printing or suitable molding process. Priorto making the plates, the catalyst or catalyst supported materials maybe sized appropriately to provide a good and broad distribution withsmall fine tail end. spraydrying or appropriate methods can also be usedto agglomerate the particles. Additional poreforming materials may beincluded. The material can be printed using 3D rapid protyping and theplates can be infused with a colloidal silica binder or a silicone resinto strengthen the body after firing. Such low temperature binders allowfor consolidation of the plates will below 1000° C. The resulting platescan be assembled as described in the disclosure or by appropriateinorganic binder such as aluminophosphate.

FIG. 20 illustrates a method of fabricating a porous ceramic article.Porous articles may comprise any of the porous plates discussed above,honeycomb filters or other porous ceramic articles. The method beginswith the step 2000 of providing a porous substrate comprising a firstmaterial composition including mullite. The mullite substrate may beformed by a 3D printing procedure, molded or other techniques. The poresmay then be infiltrated with a second material including cordieriteduring step 2002. In one example, the second material is printed,sprayed or otherwise applied to the substrate. After infiltrating, theporous ceramic article can then be formed during firing step 2004. Inone example, the second material composition has a lower melting pointthan the first material composition. As such, the general shape of theporous substrate may remain consistent while the lower melting pointmaterial integrates with the porous substrate.

As further shown in FIG. 20, as represented by arrow 2006, the substratemay be infiltrated with the second material during the step of firing.For example, cordierite material may be brought into contact with themullite substrate during the firing step wherein the melted cordieritewicks into the porous mullite, thereby infiltrating the substrate.

With respect to FIG. 20 above, high-porosity (e.g., 60% or more) ceramicarticles maybe produced by 3D printing, or other forming processes andthen may be infiltrated or partially infiltrated to form a customizedhigh strength ceramic or glass-ceramic composite. In one example, thearticles are contacted with a second ceramic or glass material with alower melting temperature during firing. In another example, thesubstrate is infiltrated with a slurry of a second C/GC material andthen fired. In still another example, batch and printing a mixture oftwo ceramic materials with differing melting temperatures may beemployed. The lower melting temperature material melts and is wickedinto the pores of the more refractory C/GC material. Distortion of theoriginal part shape can be minimal. Additionally, providing the poroussubstrate of mullite and the second material of cordierite provides thatthe cordierite has a lower melting temperature and is an effectivebonding agent that ca be used to permanently “glue” the two mullitearticles together in accordance with aspects of the disclosure discussedabove. The ability to permanently bond multiple articles (e.g., frommullite) provides the ability to fabricate a single, large structure(e.g., filter stack) from multiple small structures (e.g., porousmullite plates), thereby significantly increasing the size limit of theforming process.

Articles produced with the method illustrated in FIG. 20 and discussedabove can provide many advantages. For example, after the article isfired with the second ceramic or glass material, the article may exhibitincreased strength with minimal distortion of the article. In addition,infiltrating the pores during the process can control the porosity andweight gain of the composite article.

In example embodiments, the filter stacks may be formed by firstcreating porous ceramic plates as described herein. The relativelysimple plate design allows the plates to be formed first and can permitlayering of material that may be difficult with other ceramic filterdesigns. For example, the plate can be relatively easily constructedsuch that the composition, porosity, or pore structures varies from oneside to the other, either by layering during forming or by applyingcoatings to the formed, green disk, or after firing prior toassembly/sealing.

As described above, the relatively simple plate design also allows axialand/or radial variation of the plate. For example, the plate can haveaxial and/or radial variation of thickness, porosity, composition ordesign (e.g., inner and outer diameter) to control heat, gas flow orcatalytic function along the axial and/or radial directions. One or bothsides of the plates can also be easily treated with a catalyst or othermaterial to form coating layers, or multiple layer structures withunique filtering capabilities.

As the plates can be identical to one another, the plates may be formedfirst during a firing process. The plates can then be stacked and spacedfrom one another with compliant spacers within the filter. As such, asubsequent firing procedure can be avoided in some examples.

In further examples, a unitary filter stack may be formed by sinteringthe previously formed porous ceramic plates together. Providing twosintering procedures can provide a more controlled firing process thatmay otherwise be complicated by pore formers burning out during thefiring process. Moreover, the porous ceramic plates may be made from adifferent material than the spacing elements used to sinter the platestogether. The spacing elements, for example, may have a lowertemperature necessary to sinter the plates. The lower temperatures canallow sufficient sintering of the plates together without thermal damage(e.g., deformation) to the plates that may otherwise occur at highertemperatures. In one example, the plates are made from a mullitecomposition while the spacing elements are made from a cordieritematerial. During the second firing step, the cordierite material maysinter the mullite plates together at a temperature that is not highenough to damage the mullite plates.

Filter apparatus with unitary filter stacks may be segmented, as shownin FIG. 12, into two or more segments that are axially aligned with oneanother. Segmenting the filter can be desirable to reduce stress due tothermal gradients that might otherwise develop with a single unitaryfilter stack spanning the length of the filter apparatus.

In further examples, the filter stacks may be printed using a 3Dprinting process, dried and then fired to form the unitary structure.Such a printing process may alternately form the plates with onematerial and then the spacing elements from the same or anothermaterial. The printing process can then continue until the entire filterstack is formed. Once dried, the filter stack can then be fired to formthe unitary filter stack.

In use, the filter stacks of porous ceramic plates can providebeneficial filter characteristics such as reduced back pressure. Suchfilter designs may be used in processing various fluid streams that aregaseous, liquid or gaseous plus liquid. These fluid streams may or maynot include particulate to be filtered. Indeed, the filter designs maybe configured to purely address absorption or conversion of certaingaseous or liquid components of a fluid stream, purely to filterparticulate from the stream or may be provided for a combination ofparticulate and absorption of certain gases. Moreover, reduced thermalgradients may be experienced during regeneration processes, therebyavoiding thermal shock that may otherwise crack other ceramic filterdesigns. Moreover, the radial design of the filter may provide favorableburn-out of soot in the circumference regions of the filter because theradial flow through the filter will send more heat to those regions.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit and scope of the invention. Thus, itis intended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A filter apparatus comprising: a housing including a first fluid portand a second fluid port, a filter stack mounted within the housing andconfigured to filter a fluid stream between the fluid ports with thefilter stack defining a central flow path in fluid communication withthe first fluid port, wherein the filter apparatus includes an outerperipheral flow path in fluid communication with the second fluid portand defined between the filter stack and the housing, the filter stackincluding a plurality of porous ceramic plates axially spaced from oneanother in an axial direction of the filter apparatus by a plurality ofspacers to define a plurality of axially spaced apart radial flow areas,each porous ceramic plate including a thickness extending between afirst side and a second side of the porous ceramic plate, and eachporous ceramic plate further including a central aperture extendingthrough the thickness of the plate, the central apertures of the porousceramic plates positioned along the central flow path, wherein theplurality of axially spaced apart radial flow areas alternate in theaxial direction along the central flow path between a first set ofradial flow areas open to the central flow path and closed to the outerperipheral flow path, and a second set of radial flow areas closed tothe central flow path and open to the outer peripheral flow path.
 2. Thefilter apparatus of claim 1, wherein the plurality of spacers comprisecompliant spacers and the filter stack is compressed in the axialdirection while the compliant spacers axially bias the respective porousceramic plates from one another to maintain the respective spacingbetween the porous ceramic plates.
 3. The filter apparatus of claim 1,wherein the plurality of spacers include a first set of spacers thatclose the outer peripheral flow path from the first set of radial flowareas and a second set of spacers that close the central flow path fromthe second set of radial flow areas.
 4. The filter apparatus of claim 1,wherein at least one of the plurality of spaced apart radial flow areasare divided into a plurality of radial flow channels arranged in aradial array about the central flow path.
 5. The filter apparatus ofclaim 1, wherein the plurality of porous ceramic plates each include afilter profile defined between the first side and the second side of theporous ceramic plate, wherein at least two of the plurality of porousceramic plates have substantially different filter profiles.
 6. Thefilter apparatus of claim 1, wherein at least one of the plurality ofporous ceramic plates includes a first layer defining the first side ofthe porous ceramic plate and a second layer defining the second side ofthe porous ceramic plate, wherein the first layer and second layer havea substantially different filter profile defined between the first sideand the second side of the porous ceramic plate.
 7. The filter apparatusof claim 1, wherein at least one of the plurality of porous ceramicplates has a filter profile defined between the first side and thesecond side of the porous ceramic plate that substantially changes in aradial direction of the porous ceramic plate.
 8. The filter apparatus ofclaim 1, wherein at least one of the first side and the second side ofat least one of the plurality of porous ceramic plates define aplurality of radial flutes arranged in a radial array about thecorresponding aperture of the porous ceramic plate.
 9. The filterapparatus of claim 8, wherein each of the plurality of porous ceramicplates includes an inner periphery defining the corresponding centralaperture, and the plurality of radial flutes have a first number ofopenings at an outer periphery that is greater than a second number ofopenings at the inner periphery of the at least one of the plurality ofporous ceramic plates.
 10. The filter apparatus of claim 1, wherein eachof the radial flow areas has an axial width defined between acorresponding pair of the plurality of porous ceramic plates, whereinthe axial width of at least one of the first set of radial flow areas isgreater than the axial width of at least one of the second set of radialflow areas.
 11. The filter apparatus of claim 1, wherein first sides ofthe plurality of porous ceramic plates have corresponding filter surfaceareas that are successively larger than one another in the axialdirection.
 12. The filter apparatus of claim 1, wherein the apertures ofthe plurality of porous ceramic plates are successively smaller than oneanother in the axial direction.
 13. The filter apparatus of claim 1,wherein the plurality of porous ceramic plates alternate in the axialdirection between a first set of porous ceramic plates and a second setof porous ceramic plates, wherein each porous ceramic plate of the firstset of plates includes an outer peripheral edge configured to nestwithin a corresponding porous ceramic plate of the second set of plates.14. The filter apparatus of claim 1, wherein the plurality of porousceramic plates alternate in the axial direction between a first set ofporous ceramic plates and a second set of porous ceramic plates, whereineach porous ceramic plate of the first set of plates includes a centralcollar portion configured to be received within the central aperture ofa corresponding porous ceramic plate of the second set of porous ceramicplates.
 15. A filter apparatus comprising: a filter stack including aplurality of porous ceramic plates that each include a central aperturepositioned along a central flow path, the plurality of porous ceramicplates are axially spaced from one another in an axial direction of thefilter apparatus to define a plurality of axially spaced apart radialflow areas that alternate in the axial direction between a first set ofradial flow areas that are open to the central flow path, and a secondset of radial flow areas that are closed to the central flow path,wherein the plurality of porous ceramic plates alternate between a firstset of porous ceramic plates that are nested with a second set of porousceramic plates.
 16. The filter apparatus of claim 15, wherein eachporous ceramic plate of the first set of plates includes an outerperipheral edge configured to nest within a corresponding porous ceramicplate of the second set of plates.
 17. The filter apparatus of claim 15,wherein each porous ceramic plate of the first set of plates includes acentral collar portion configured to be received within the centralaperture of a corresponding porous ceramic plate of the second set ofporous ceramic plates.
 18. A filter apparatus comprising: a filter stackincluding a plurality of porous ceramic plates that each include acentral aperture positioned along a central flow path, the plurality ofporous ceramic plates are axially spaced from one another in an axialdirection of the filter apparatus to define a plurality of axiallyspaced apart radial flow areas that alternate in the axial directionbetween a first set of radial flow areas that are open to the firstcentral flow path, and a second set of radial flow areas that are closedto the first central flow path, wherein each of the plurality of porousceramic plates include a first side and a second side, with at least oneof the sides defining a plurality of radial flutes arranged in a radialarray about the corresponding aperture of the porous ceramic plate toincrease the filtration surface area of the side with the radial flutes.19. The filter apparatus of claim 18, wherein the at least one of thesides of each of the plurality of porous ceramic plates includes afilter surface that undulates about the corresponding central apertureto define the plurality of radial flutes.
 20. The filter apparatus ofclaim 18, wherein each of the plurality of porous ceramic platesincludes an inner periphery defining the corresponding central aperture,and the plurality of radial flutes have a first number of openings at anouter periphery that is greater than a second number of openings at theinner periphery of the corresponding porous ceramic plate.